Mixtures comprising monoethylene glycol and diethylenetriamine are obtained, for example, in the process for preparing ethyleneamines and ethanolamines by hydrogenating amination of monoethylene glycol (hereinafter: MEG) in the presence of a catalyst.
In known processes, a mixture of ethanolamines and ethyleneamines is generally obtained; among these, especially ethylenediamine (hereinafter: EDA) and diethylenetriamine (bis(2-aminoethyl)amine; hereinafter: DETA) are important valuable substances whose uses include use as solvents, stabilizers, for synthesis of chelating agents, synthetic resins, medicaments, inhibitors and interface-active substances.
EDA is used in particular as a raw material for fungicides and insecticides,
DETA finds use in particular as a solvent for dyes and is a starting material for preparing ion exchangers, pesticides, antioxidants, corrosion protectants, complexing agents, textile assistants and absorbents for (acidic) gases.
Nonlinear amines in the product mixture of the ethyleneamines and ethanolamines and especially cyclic amines, predominantly piperazine and piperazine derivatives, are, in contrast, less valued to unwanted.
For the preparation of ethyleneamines, numerous processes are described in the literature.
According to PEP Report No. 138, “Alkyl Amines”, SRI International, 03/1981, in particular pages 7, 8 13-16, 43-107, 113, 117, the reaction of dichloroethane with ammonia at molar ratios of 1:15 affords DETA with a proportion of the ethyleneamines formed of greater than 20% by weight. In addition to 40% by weight of EDA, however, 40% by weight of higher ethyleneamines are obtained.
Amination of monoethanolamine (hereinafter: MEOA) with ammonia (cf., for example, the abovementioned PEP Report, U.S. Pat. No. 4,014,933 (BASF AG)) allows the formation of these higher ethyleneamines (i.e. ethyleneamines having a boiling point above that of triethylenetetramine (hereinafter: TETA)) to be substantially suppressed in favor of EDA. However, the by-products obtained in this reaction are aminoethylethanolamine (hereinafter: AEEA) and piperazine (hereinafter: PIP).
Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, pages 399-407, (C. M. Barnes et al.) describes the ammonolysis of MEOA to EDA over nickel catalysts on an SiO2—Al2O3 mixed support. Addition of water and the powdered catalyst were purportedly advantageous in increasing the yield of EDA.
U.S. Pat. No. 4,855,505 discloses a process for hydroaminating monoethylene glycol for example with ammonia for example in the presence of a catalyst which comprises from 4 to 40% by weight of nickel or cobalt and from 0.1 to 5% by weight of ruthenium which has been introduced as a solution of a ruthenium halide on a porous metal oxide support comprising at least 50% by weight of activated alumina. The catalyst is used, by way of example, in the form of tablets having a length and a diameter of about 3 mm.
The product streams obtained in the processes described are separated by distillation to obtain the individual products in pure form, in particular the particularly desired EDA and DETA. A problem here is that MEG and DETA form an azeotrope which is virtually independent of the pressure and therefore cannot be separated by pressure swing distillation. The azeotropic composition is approx. 44% by weight of MEG and 56% by weight of DETA and has a boiling point at 150 mbar of 154° C., compared to the boiling point of pure MEG of 144° C. and of pure DETA of 142° C., in each case at the pressure stated above of 150 mbar.